Of lasers used to, for example, cut a member and weld members together, YAG lasers, YVO4 lasers, fiber lasers, and other similar lasers have a semiconductor laser (laser diode: LD) as an excitation light source. For example, excitation light of a semiconductor laser whose wavelength is in an 800-nm band or a 900-nm band is irradiated onto a laser medium directly or via an optical fiber to be converted into oscillating light whose wavelength is in a 1,000-nm band. Cases of using laser light of a semiconductor laser whose wavelength is in a 900-nm band or a 1,000-nm band directly to process a member are also found in recent years.
High-energy laser light is required to process a member, and power enhancement is consequently demanded of semiconductor lasers that generate excitation light as well. An LD bar in which a plurality of light emitting layers (active layer stripes) of semiconductor elements are aligned in a one-dimensional direction is thus used in order to enhance the power of a semiconductor laser. For example, ten to fifty beams of laser light are emitted in parallel from an end surface of each light emitting layer in an LD bar having a width of approximately 10 nm and including light emitting layers each of which is from 50 μm to 200 μm in width and which are laid side by side at equal pitches. A power of several tens of watts is obtained from such an LD bar and, in recent years, even LD bars having a power of several hundreds of watts are available.
When laser light emitted from the LD bar described above is used by, for example, causing the laser light to enter an optical fiber or irradiating the laser light directly onto a processing object, it is common to parallelize, that is, collimate, the laser light once. A light emitting layer of a semiconductor element is approximately 1 μm in thickness while the width of the light emitting layer is from 50 μm to 200 μm, which leads to a significant difference in the divergence angle of the laser light between a width direction of the light emitting layer and a thickness direction of the light emitting layer, with the divergence angle in the width direction being from 7 deg to 11 deg and the divergence angle in the thickness direction being from 45 deg to 60 deg. The thickness direction, in which the divergence angle of the laser light is large, is called a fast axis direction, and the width direction, in which the divergence angle of the laser light is small, is called a slow axis direction.
A beam shaping device has hitherto been proposed in which, in order to collimate a plurality of beams of laser light emitted from a semiconductor laser, cylindrical lenses are placed separately for the fast axis direction and for the slow axis direction, and a plurality of cylindrical lenses corresponding to the respective beams of laser light are arranged to form a cylindrical lens array for the slow axis direction (see Patent Literature 1, for example). In this type of beam shaping device of the related art, beams of laser light emitted from a plurality of light emitting layers can be collimated individually in the slow axis direction, and laser light in the fast axis direction and laser light in the slow axis direction can be collimated separately as well. A collimator lens in the fast axis direction is called a fast axis collimator (FAC), and a collimator lens in the slow axis direction is called a slow axis collimator (SAC).
Another beam shaping device has hitherto been proposed in which, in order to collimate laser light emitted from an LD bar, beams of laser light transmitted through an FAC are each rotated by 90 deg about an optical axis by a light path conversion element to be switched between the fast axis direction and the slow axis direction, and then enter an SAC (see Patent Literature 2, for example). In this type of beam shaping device of the related art, differences in the quality of laser light between the fast axis direction and the slow axis direction, namely, differences in laser light width and in divergence angle, can be kept small when the laser light is irradiated onto a laser medium or when the laser light enters an optical fiber.